Method for producing aliphatic oligocarbonate diols

ABSTRACT

A process for the production of aliphatic oligocarbonate diols is disclosed. The optionally catalyzed high yield process entails the multistage transesterification of aliphatic diols with dimethyl carbonate. In the process DMC-methanol mixtures that have been distilled off are recycled to the reaction solution with further conversion and depletion of the contained DMC in the same or in a following reaction batch.

The present invention relates to a new process for the production ofaliphatic oligo-carbonate diols from aliphatic diols by a multistagetransesterification with dimethyl carbonate (DMC) with an almostcomplete consumption of the carbonate that is used. The processaccording to the invention enables a particularly high-yield productionof aliphatic oligocarbonate diols to be achieved starting from easilyaccessible DMC.

Aliphatic oligocarbonate diols have been known for a long time asimportant intermediate products, for example in the production ofplastics, lacquers and adhesives, for example by reaction withisocyanates, epoxides, (cyclic) esters, acids or acid anhydrides. Theycan be obtained in principle from aliphatic diols by reaction withphosgene (e.g. DE-A 1 595 446), bis-chlorocarbonic acid esters (e.g.DE-A 857 948), diaryl carbonates (e.g. DE-A 1 915 908), cycliccarbonates (e.g. DE-A 2 523 352: ethylene carbonate) or dialkylcarbonates (e.g. DE-A 2 555 805).

Of the carbonate sources, diphenyl carbonate (DPC) belonging to thediaryl carbonates is of particular importance since aliphaticoligocarbonate diols of particularly high quality can be produced fromDPC (e.g. U.S. Pat. No. 3,544,524, EP-A 292 772). In contrast to forexample aliphatic carbonate sources, DPC reacts quantitatively withaliphatic OH groups so that, after removal of the phenol that is formed,all terminal OH groups of the oligocarbonate diol are available forreaction with for example isocyanate groups. In addition only very smallconcentrations of soluble catalyst are required, with the result thatthe latter can remain in the product.

The processes based on DPC have the following disadvantages however:

Only ca. 13% of the DPC remains in the product, the remainder beingdistilled off as phenol. Depending on the respective alkyl radical, asubstantially higher proportion of the dialkyl carbonates remains in thesubsequent product. For example, ca. 31% of the dimethyl carbonate (DMC)remains in the subsequent product, since the methanol that is distilledoff has a substantially lower molecular weight than phenol.

Accordingly, due to the fact that high boiling point phenol (normalboiling point: 182° C.) has to be separated from the reaction mixture,only diols having a boiling point that is considerably above 182° C. canbe used in the reaction in order to avoid the diol being unintentionallydistilled off.

Dialkyl carbonates, in particular dimethyl carbonate (DMC), as startingcomponents are characterised by a better availability on account oftheir ease of production. For example, DMC can be obtained by directsynthesis from MeOH and CO (e.g. EP-A 0 534 454, DE-A 19 510 909).

Numerous patent applications (e.g. U.S. Pat. No. 2,210,817, U.S. Pat.No. 2,787,632, EP-A 364 052) relate to the reaction of dialkylcarbonates with aliphatic diols:

It is known from the state of the art to mix aliphatic diols togetherwith a catalyst and the dialkyl carbonate (e.g. diethyl carbonate,diallyl carbonate, dibutyl carbonate) and distil off the alcohol that isformed (ethanol, butanol, allyl alcohol) from the reaction vesselthrough a column. The higher boiling point, co-evaporated dialkylcarbonate is separated in the column from the lower boiling pointalcohol and is recycled to the reaction mixture.

In contrast to DPC, dialkyl carbonates do not react quantitatively withaliphatic OH groups since the transesterification of two aliphaticalcohols involves an equilibrium reaction. Thus, after the removal ofthe alcohol that is formed a proportion of the desired terminal OHgroups are present not as OH groups but as alkoxycarbonyl terminalgroups (—OC(O)—OR2 group in formula I, wherein R2 denotes an alkylradical and R1 denotes an alkylene radical).

These alkoxycarbonyl terminal groups are unsuitable for further reactionwith for example isocyanates, epoxides, (cyclic) esters, acids or acidanhydrides. The reaction is therefore completed by applying a vacuum inorder to de-cap and remove the alcohol that is formed. The reactionmixtures are normally heated and stirred in vacuo in order to achievethis objective, although the quality of oligocarbonate diols that can beachieved is not as good as is obtained by reaction with DPC.

EP-A 0 364 052 describes for example a process in which a degree ofutilisation of the terminal OH groups of only ca. 97% is achieved at200° C. and under a vacuum of ca. 50 Torr (ca. 66 mbar). Even underconsiderably more drastic conditions the degrees of utilisation of theterminal OH groups can be increased only insignificantly. At 1 Torr (ca.1.3 mbar) degrees of utilisation of only ca. 98% are achieved (EP-A 0798 328).

The use of dimethyl carbonate (DMC) to produce aliphatic oligocarbonatediols has been known only for a fairly short time despite its goodaccessibility (e.g. U.S. Pat. No. 5 171 830, EP-A 798 327, EP-A 798 328,DE-A 198 29 593).

When using DMC to produce oligocarbonate diols low boiling pointazeotropic DMC-methanol mixtures are formed that contain, depending onthe pressure, ca. 20 to 30 wt. % of DMC (ca. 30 wt. % at normalpressure). A relatively large effort and expenditure is required toseparate these azeotropic mixtures into methanol and DMC (e.g. membraneseparation). The DMC that is azeotropically distilled off is accordinglylost to the reaction and is no longer available for a completeconversion. The lost DMC therefore has to be replenished by additionalfresh DMC.

In EP-A 0 358 555 and U.S. Pat. No. 4,463,141 it is for example inaddition simply recommended to take into account, during the weighingin, the amount of DMC that is azeotropically distilled off.

In EP-A 0 798 328 the corresponding diol component is reacted with DMCaccompanied by distillation of the azeotropic mixture. The subsequentde-capping takes place under vacuum distillation, whereby under verydrastic vacuum conditions (I Torr, ca. 1.3 mbar) degrees of utilisationof the terminal OH groups of ca. 98% can be achieved (EP-A 0 798 328:Table 1). No details of the remaining azeotropic mixture and the loss ofthe DMC are given.

EP-A 798 327 describes a two-stage process in which a diol is first ofall reacted with an excess of DMC with distillation of the azeotropicmixture to form an oligo-carbonate whose terminal OH groups arecompletely inaccessible, being methoxycarbonyl terminal groups. Afterremoval of the catalyst and distillation of the excess DMC in vacuo (65Torr, 86 mbar), the oligocarbonate diol is obtained in a second stage byadding further amounts of the diol and a solvent (e.g. toluene) asentrainment agent for the methanol that is formed. Solvent residues thenhave to be distilled off in vacuo (50 Torr, 67 mbar). The degree ofutilisation of the terminal OH groups according to this process is onlyca. 97%. The disadvantage of this process is that it is complicated dueto the use of a solvent and due to the multiple distillation, low degreeof utilisation of the terminal OH groups, as well as the very high DMCconsumption.

In DE-A 198 29 593 a diol is reacted with DMC, the methanol that isformed being distilled off. This publication does not give any detailsof the overall azeotropic distillation procedure, apart from a singlemention of the word “azeotrope” in the Table “Flow chart of the processaccording to the invention”. Claim 1c states that the molar ratio ofmethanol to DMC in the distillate is between 0.5:1 and 99:1. The DMCcontent in the methanol that is distilled off is accordingly between 85wt. % and 2.8 wt. %. As a detailed analysis shows (see below), in DE-A198 29 593 DMC is in fact also used in excess and is distilled offazeotropically. Accordingly, ca. 27.8% of the DMC that is used is lost.

As Comparison Example 1 shows (see below), DMC contents in thedistillate of less than 20% can be achieved only at high catalystconcentrations (ca. 0.15% Ti(O-iPr)₄, corresponding to ca. 250 ppm Ti)and very long reaction times. At these high catalyst concentrations thecatalyst cannot be left in the product after the end of the reaction,but has to be neutralised. In DE-A 198 29 593 the catalyst (Example 1:0.15% Ti(O-nBu)₄ and Example 2: 0.12% Ti(O-nBu)₄) is neutralised ormasked by adding phosphoric acid.

The DMC content in the distillate increases with falling catalystconcentration (Comparison Example 1). Consistently low DMC contents inthe distillate can be achieved only by drastically increasing thereaction time. With a reduced catalyst concentration of ca. 0.01%Ti(O-iPr)₄ (ca. 16 ppm Ti) the catalyst can remain in the product afterthe end of the reaction. As Comparison Example 1 shows, this leadshowever to industrially no longer practicable reaction timesrespectively DMC contents of 22 to 30% in the distillate.

In DE-A 198 29 593 no details are given concerning the degree ofutilisation of the terminal OH groups.

In U.S. Pat. No. 5,171,830 butanediol-1,4 is first of all heated withDMC under reflux and then the volatile constituents are distilled off(azeotropically). After vacuum distillation under drastic conditions (1Torr, 1.3 mbar), taking up the product in chloroform, precipitating theproduct with methanol and drying the product, an oligocarbonate diol isobtained in 55% of the theoretical yield (Example 6). No details aregiven concerning the degree of utilisation of the terminal OH groups andthe azeotropic distillation procedure.

German Patent Application 1999 00 554.0 describes a process in which thetransesterification of the diol with DMC is carried out by reactiverectification in a gas-liquid countercurrent apparatus. Due to thecountercurrent procedure the methanol-DMC azeotropic mixture can beavoided and a DMC conversion of ca. 95% can be achieved. In order tode-cap the OH terminal groups nitrogen is passed through the product asstripping gas under a low vacuum (ca. 150 mbar) (2 to 200 Nl/h(Nl=normal liter)). By means of the stripping the methanol can belargely removed, the transesterification can be completed, and degreesof utilisation of the terminal OH groups of ca. 99.8% can be achieved.

None of the previously known publications describe industrially easilyrealisable processes for reacting DMC with aliphatic diols to formoligocarbonate diols with high space-time yields, almost completeconversion and with high degrees of utilisation of the terminal OHgroups. The inevitable occurrence of DMC-methanol mixtures of varyingcomposition and the associated loss of DMC considerably reduce theattractiveness of the described processes.

The object of the invention is accordingly to provide a simple,high-yield process that can also be carried out on an industrial scale,that enables oligocarbonate diols to be produced by transesterificationof aliphatic diols with dimethyl carbonate, optionally with the use ofsuch a small amount of catalyst that this can remain in the productafter the end of the reaction, with good space-time yields, in simpleapparatus, and with almost complete utilisation of the carbonate that isemployed.

It has now surprisingly been found that the production of aliphaticoligocarbonate diols can be successfully achieved by reacting aliphaticdiols with dimethyl carbonate, optionally accelerated by catalysts, witha degree of conversion of the DMC that is used of more than 80%, whereinin a multistage process DMC-methanol mixtures that have been distilledoff are recycled to the reaction solution with further conversion anddepletion of the contained DMC.

The present invention accordingly provides a process for the productionof aliphatic oligocarbonate diols by reacting aliphatic diols withdimethyl carbonate, optionally accelerated by catalysts, with a degreeof conversion of the DMC that is used of more than 80%, characterised inthat in a multistage process DMC-methanol mixtures that have beendistilled off are recycled to the reaction solution with furtherconversion and depletion of the contained DMC in the same or in asubsequent reaction batch.

In the execution of the process according to the invention for producingaliphatic oligocarbonate diols by reacting aliphatic diols with dimethylcarbonate, the mixture of DMC and MeOH that has been distilled off in abatch is re-used at the start of a following reaction batch. ThisDMC-methanol mixture that has been distilled off is thus re-used withfurther conversion of the contained DMC. Accordingly, the DMC of thepreviously collected and re-used mixture is depleted, and distillatesare formed having reduced DMC contents.

The process according to the invention can be carried out as a two-stageor multi-stage process.

In order to achieve an almost complete conversion of the employed DMC ina multi-stage procedure, the process according to the invention iscarried out as follows:

In a for example two-stage batch procedure the respective diol componentis added to the vessel together with a catalyst in the first stage, andthe (for example azeotrope) DMC-methanol mixture that has been formedand collected during a preceding batch process is added slowly thereto,preferably under the surface, for example through a dip tube. Dependingon the feed rate, a distillate containing DMC in an amount of between0.5 and 20%, preferably between 1.5 and 10%, and particularly preferablybetween 3 and 7%, is obtained at the head even of a short column.

In the second stage the residual amount of DMC, which results from theamount of DMC predetermined by the stoichiometry of the desired endproduct and the amount of DMC already added to the first stage of thereaction, is rapidly fed into the vessel and the DMC-methanol mixturethus distilled off over a large column (e.g. azeotropically) iscollected.

The composition of all distillates is determined, and the loss of DMCthat has occurred due to the distilling off of the DMC-methanol mixturesin the first and second stages is replenished in a subsequent stage byadding pure DMC. The distilled-off azeotrope consisting of DMC and MeOHis also collected and re-used in the first stage together with thedistillate from the second stage in a subsequent reaction batch.

A de-capping of the terminal groups is necessary in order to achieve adegree of utilisation of the OH terminal groups of >99%.

In order to de-cap the terminal groups (utilisation of the terminal OHgroups), the last residues of methanol and traces of dimethyl carbonatecan be removed from the product. For example by passing in an inert gas(e.g. N₂) into the oligocarbonate diol, gas bubbles are generated in theproduct, optionally at an only slight vacuum of e.g. ca. 150 mbar, thatin the product are saturated with methanol and/or DMC. The methanol isthus almost completely expelled from the reaction batch. By strippingwith an inert gas the equilibrium can be displaced still further infavour of the product by the removal of the methanol, the esterificationcan be brought to completion, and thus the terminal groups can beutilised. The quality of the resultant oligocarbonate diol can thus beraised to the level of DPC-based oligocarbonate diols, and the degree ofutilisation of the terminal OH groups rises to more than 98%, preferablyto 99.0 to 99.95%, and particularly preferably to 99.5 to 99.9%.

The distillates with the low DMC contents can be discarded, used assolvents or wash liquids in other processes, converted by aqueoushydrolysis into methanol and used further or thermally exploited assuch, or can also be used in the process according to the invention in amultistage procedure with further depletion of the DMC content.

In a three-stage variant of the process according to the invention forexample these mixtures may be used as follows: a ca. 5% DMC-methanolmixture that has been collected in the second stage of the precedingreaction batch is used for example in a first stage. A further depletionof the DMC in the distillate to 0.3% to 5%, preferably to 0.8% to 4%,particularly preferably to 1.5% to 3%, is thereby achieved. Thesedistillates are discarded or—as previously described—are utilisedfurther. The DMC-methanol mixture containing for example ca. 30% DMCthat was formed in the previous batch in the third stage is used in thesecond stage. A distillate containing for example ca. 5% DMC is thenobtained in this case. This distillate is used in the first stage in thenext batch. In the third stage pure DMC is added to the reactor, aDMC-methanol mixture containing for example 30% DMC again being formed,which is employed in the second stage of the following batch. The amountof DMC of the third stage is chosen so that the sum of the DMC amountsof all three stages after distilling off the DMC-methanol mixtures thencorresponds to the amount predetermined by the desired stoichiometry. Inthe three-stage procedure it is therefore possible to achieve an almostquantitative utilisation of the employed DMC by recycling the distillatetwice.

By appropriate repetition the process can also be carried out in morethan three stages, and in fact up to n stages (where n is an integergreater than or equal to 2).

In principle a discontinuous batch procedure or a continuous procedureis possible according to the process of the invention. The batchprocedure described above is only one example and should not beunderstood as restrictive. The person skilled in the art knows inprinciple how to carry out such processes in a fully continuous manner.

The addition of the DMC-methanol mixture and/or of the pure DMC can beeffected in the process according to the invention also by repeatedrepumping of the distillate: distillates forming during the metering inprocedure are returned to the pump vessel, where they are collected andreintroduced to the reactor. DMC-methanol mixture or pure DMC is thuscontinuously metered into the reactor from a pump vessel, a DMC-depletedmixture being distilled off and collected in the same vessel. The DMCconcentration of the mixture in the vessel therefore constantly falls.In this connection the metering in rate is chosen to be higher by amultiple (e.g. ca 4 to 10 times higher) than in a simple metering inprocedure. When the DMC content of the distillate has fallen to thedesired value, the further addition of the DMC-methanol mixture or ofthe DMC to the reactor is stopped and the mixture is distilled furtheruntil the total amount of DMC and methanol has been distilled off andcollected in the pump vessel.

Two vessels may also be employed when repumping the DMC-methanolmixtures or the DMC: a DMC-methanol mixture or pure DMC is passed fromvessel 1 at a multiple rate (e.g. ca 4- to 10-fold rate) into thereactor and the distillate formed is collected in vessel 2. On accountof the higher pumping rate this mixture does not reach the low DMCcontents as previously, but instead is only somewhat depleted in DMC(for example ca. 10% to 28% depending on the catalyst concentration whenusing a ca. 32% DMC-methanol mixture Example 8). After all theDMC-methanol mixture or the DMC has been fed from vessel 1 into thereactor, the DMC-methanol collected in vessel 2 is passed, under thesurface, into the reactor. The distillate that is now formed iscollected in vessel 1. The change of vessels is repeated until the DMCcontent of the distillate has fallen below a desired value (for exampleca. 3-5%). The distillates are thus fed under an in each case smallerdepletion of the DMC, and thus more frequently, into the reactor.

In a further variant of the process according to the invention the laststage (for example the second stage in a two-stage process), in whichpure DMC is rapidly metered in under distillation of the azeotropicmixture, is carried out in two partial stages: in the first partialstage the pure DMC is metered in sufficiently slowly so that not theazeotrope is distilled off, but instead a DMC-methanol mixture with forexample ca. 5 to 8% DMC. This distillate is—like the distillate of thefirst stage—either discarded or, as described previously, used further.As Comparison Example 1 shows, the DMC content of the distillateincreases with increasing reaction time on metering in the DMC. When acertain threshold value is exceeded, the remaining DMC is then added soquickly in the second partial stage that azeotropic DMC-methanolmixtures are distilled off. These mixtures are then collected and usedfurther in a following reaction batch. The other stages in whichDMC-methanol mixtures are introduced may likewise be carried out inseveral partial stages with different feed rates.

The process according to the invention (reaction and distillation underthe addition of DMC-methanol mixtures or DMC) is in principle carriedout under a light vacuum, under normal pressure, or at elevatedpressure. The reaction is preferably carried out a pressure of 0.4 to100 bar, preferably 0.7 to 15 bar, particularly preferably at a pressureof 1 to 6 bar and—depending on the respective pressure—at temperaturesof 100 to 300° C., preferably at temperatures of 160 to 240° C. In thisconnection an elevated pressure leads, on account of the betterazeotropic point (e.g. ca. 20% DMC/80% MeOH at 4 bar) to a betterconversion of DMC and thus shorter reaction times, and also to lower DMCcontents in the distillate.

The DMC content of the distillate when using a DMC-methanol mixture orpure DMC depends in each case on the feed rate and reaction time, and onthe amount of catalyst: an increase in the catalyst concentration and/ora reduction in the feed rate of the DMC-methanol mixture or of the DMC(increase in the reaction time) leads to a reduction of the DMC contentin the distillate. A lowering of the catalyst concentration and/or areduction in the reaction time results in a higher DMC content in thedistillate.

The amount of DMC that has been removed from the reaction batch bydistillation is determined by measuring the DMC contents of theindividual distillates. This missing amount must be added in the form ofpure DMC to the batch before stripping the methanol with inert gasesunder a vacuum in order to utilise the terminal groups. A mixture of DMCand methanol is again formed. This lost DMC is replenished, a proportionbeing distilled off again. With each new addition the amount of DMCdistilled off becomes less, and accordingly the desired stoichiometry isapproached (Example 2). This complicated procedure can be simplifiedconsiderably by combining the individual subsequent stages: the amountsof DMC that are distilled off in the individual subsequent stages areknown or may be calculated beforehand from previous batches—for examplein the first batch—so that the complete amount of DMC can be added in asingle stage (Example 3, composition of the second stage and subsequentstages).

A small amount of DMC is lost when inert gas bubbles are pumped induring the distillation of the methanol and the de-capping of the OHterminal groups at the end of the reaction. This amount must be takeninto account beforehand in the addition of DMC. This amount may bedetermined from the empirical values of the previous batches.

Alternatively, a small excess of DMC may be added beforehand so that,after the distilling off of the azeotrope and after the de-capping bystripping of the last residues of methanol and DMC by passing in aninert gas (e.g. N₂) under a slight vacuum (ca. 150 mbar), a slightexcess of DMC remains in the product or is bound as ester. After thestripping a product is thus obtained that exhibits a completefunctionality of the terminal OH groups but in which the degree ofpolymerisation is too high. The correction is then made by adding afurther amount of the diol component and carrying out a new, shortesterification stage (Example 4). The correction amount may bedetermined on the one hand via the mass balance—determination of the DMCamounts in all distillates and comparison with the total amount added—ormay be determined from a measurable property (e.g. OH number, viscosity,average molecular weight, etc.) of the product whose degree ofpolymerisation is too high. A renewed de-capping is not necessary afterthe correction since all terminal OH groups were already free before thecorrection and no renewed capping is caused by adding the diolcomponents.

A correction by adding DMC after the de-capping by gassing with an inertgas in the case of a product containing too little DMC leads to arenewed build-up of the capping.

The process according to the invention thus comprises the followingprocess stages in the two-stage variant:

addition of the diol components and optionally the catalyst to thereactor,

1^(st) stage: introduction of the DMC-methanol mixture (for example theazeotrope) from the previous batch and reaction of the DMC containedtherein, distilling off of a DMC-methanol mixture with—depending on thereaction conditions—for example 3 to 7% of DMC, or if desired multiplepumping of the distillate until the DMC content has fallen to thedesired value,

2^(nd) stage: introduction and reaction of pure DMC. The amount of DMCis chosen so that, after distilling off, exactly the required amount ofDMC or alternatively a slight excess remains in the reaction solution inall stages (addition of the DMC-methanol mixture (e.g. azeotrope),addition of DMC and de-capping). If desired the complete amount of DMCmay be metered in rapidly in one stage or in two partial stages: in thefirst case a DMC-methanol mixture (e.g. the azeotrope) is distilled off,collected, and re-used in the first stage in a following batch. In thesecond case the DMC is metered in sufficiently slowly in the fistpartial stage that DMC-methanol mixtures with low DMC contents areobtained, and in the second partial stage—after an increase of the DMCcontent in the distillate—the DMC is then rapidly metered in so that aDMC-methanol mixture having a higher DMC content (e.g. the azeotrope) isformed, which is re-used in a following batch,

optional de-capping: utilisation of the terminal OH groups bydischarging the last methanol and/or DMC residues, for example bygenerating gas bubbles (for example introduction of inert gases such asN₂), for example under a slight vacuum (e.g. ca. 150 mbar),

optional correction: correction of the stoichiometry by adding furtheramounts of the diol components and renewed brief esterification.

In the first batch, in which no DMC-methanol mixtures are yet availablefrom the previous batches, in principle only pure DMC may be used, withthe result that on distillation only a DMC-methanol mixture (e.g. theazeotrope) is formed that is re-used in the first stage in the secondbatch, or if desired a DMC-methanol mixture (e.g. the azeotrope) isprepared by mixing DMC and methanol in the expected amounts.

Aliphatic diols with 3 to 20 C atoms in the chain are used in theprocess according to the invention. The following compounds may bementioned by way of example, although this is not a complete list:1,7-heptanediol, 1,8-ocatanediol, 1,6-hexanediol, 1,5-pentanediol,1,4-butanediol, 1,3-butanediol, 1,3-propanediol,2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol,2-methyl-pentanediol, 2,2,4-trimethyl-1,6-hexanediol,0.3,3,5-trimethyl-1,6-hexanediol. 2,3,5-trimethyl-1,6-hexanediol,cyclo-hexanedimethanol, etc. as well as mixtures of various diols.

Furthermore the addition products of the diols with lactones (esterdiols) such as for example caprolactone, valerolactone, etc., may beused as well as mixtures of the diols with lactones, an initialesterification of lactone and the diols not being necessary.

Moreover there may be used the addition products of the diols withdicarboxylic acids, such as for example: adipic acid, glutaric acid,succinic acid, malonic acid, etc. or esters of dicarboxylic acids aswell as mixtures of diols and dicarboxylic acids or esters ofdicarboxylic acids, a preliminary transesterification or dicarboxylicacid and diols not being necessary.

Polyether polyols may furthermore be used, such as for examplepolyethylene glycol, polypropylene glycol, polybutylene glycol as wellas polyether polyols that have been obtained by copolymerisation of forexample ethylene oxide and propylene oxide, or polytetramethylene glycolthat has been obtained by ring-opening polymerisation of tetrahydrofuran(TBF).

Mixtures of various diols, lactones and dicarboxylic acids may be used.

1,6-hexanediol, 1,5-pentanediol and mixtures of 1,6-hexanediol andcaprolactone are preferably used in the process according to theinvention.

As catalysts there may in principle be used all soluble catalysts knownfor transesterification reactions (homogeneous catalysis), as well asheterogeneous transesterification catalysts. The process according tothe invention is preferably carried out in the presence of a catalyst.

Particularly suitable for the process according to the invention arehydroxides, oxides, metal alcoholates, carbonates and organometalliccompounds of metals of main groups I, II, III and IV of the PeriodicSystem of the Elements, of subgroups III and IV, as well as the elementsof the rare earth group, in particular compounds of Ti, Zr, Pb, Sn andSb.

The following may be mentioned by way of example: LiOH, Li₂CO₃, K₂CO₃,KOH, NaOH, KOMe, NaOMe, MeOMgOAc, CaO, BaO, KOt-Bu, TiCl₄, titaniumtetraalcoholates or terephthalates, zirconium tetraalcoholates, tinoctanoates, dibutyltin dilaureate, dibutyltin oxide, dibutyltinmethoxide, bistributyltin oxide, tin oxalates, lead stearates, antimonytrioxide, zirconium tetra-iso-propylate, etc. Inorganic or organic acidsmay furthermore be used as catalysts, for example phosphoric acid,acetic acid, p-toluenesulfonic acid.

There may furthermore be used in the process according to the inventiontertiary amines R₁R₂R₃N where R₁₋₃ denotes C₁-C₃₀-hydroxyalkyl, -aryl or-alkyl, in particular trimethylamine, triethylamine, tributylamine,N,N-dimethylcyclohexylamine, N,N-dimethylethanolamine,1,8-diazabicyclo-(5.4.0)undec-7-en, 1,4-diazabicyclo-(2.2.2)-octane,1,2-bis(N,N-dimethylamino)ethane, 1,3-bis(N,N-dimethylamino)propane andpyridine.

Preferably the alcoholates and hydroxides of sodium and potassium (NaOH,KOH, KOMe, NaOMe), the alcoholates of titanium, tin or zirconium (e.g.Ti(OPr)₄), as well as organotin compounds are used, the titanium, tinand zirconium tetra-alcoholates preferably being used with diols thatcontain ester functions or mixtures of diols with lactones.

In the process according to the invention the homogeneous catalyst isoptionally used in concentration (specified in weight percent of metalreferred to aliphatic diol that is used) of up to 1000 ppm (0.1%),preferably between 1 ppm and 500 ppm, particularly preferably 5 to 100ppm. The catalyst may be left in the product after the end of thereaction or may be separated, neutralised or masked. The catalyst ispreferably left in the product.

The removal of the methanol for the de-capping of the terminal groupsmay take place for example by heating the reaction mixture in vacuo,preferably by producing gas bubbles in the apparatus. These gas bubblesmay be generated by passing inert gases such as nitrogen, argon,methane, ethane, propane, butane, dimethyl ether, dry natural gas or dryhydrogen into the reactor, wherein the methanol-containing and dimethylcarbonate-containing gas stream leaving the oligocarbonate may be addedagain to the oligocarbonate for the saturation.

These gas bubbles may also be produced by passing in inert, low boilingpoint liquids such as pentane, cyclopentane, hexane, cyclohexane,petroleum ether, diethyl ether or methyl-tert.-butyl ether, wherein thesubstances may be passed in in liquid or gaseous form and themethanol-containing and dimethyl carbonate-containing gas stream leavingthe oligocarbonate may be partially added again to the oligocarbonatefor the saturation. Preferably nitrogen is used.

The substances used to produce gas bubbles may be added to theoligocarbonate through simple dipping tubes, preferably by means ofannular nozzles or gassing stirrers. The degree of utilisation of theterminal OH groups that is achieved depends on the duration of thede-capping, and on the amount, size and distribution of the gas bubbles:with increasing duration of the de-capping and better distribution (forexample better distribution and larger interface due to larger numbersof smaller gas bubbles when the latter are introduced through a gassingstirrer), the degree of utilisation is improved. When introducing forexample nitrogen (150 mbar, 40 Nl/h) through a gassing stirrer, afterone hour a degree of utilisation of ca. 99% is achieved, and after 5 to10 hours a degree of utilisation of 99.8% is achieved.

The de-capping by producing inert gas bubbles in the oligocarbonate diolis carried out at temperatures of 130° C. to 300° C., preferably attemperatures of 200° C. to 240° C., and at pressures of 0.01 to 1000mbar, preferably at pressures of 30 to 400 mbar, particularly preferablyat pressures of 70 to 200 mbar.

The molecular weight of the oligocarbonate diols produced by the processaccording to the invention is adjusted via the molar ratio of diol toDMC, the molar ratio of diol to DMC being between 1.01 and 2.0,preferably between 1.02 and 1.8, and particularly preferably between1.05 and 1.6. The specified ratio describes of course the stoichiometryof the product, i.e. the effective ratio of diol to DMC after distillingoff the DMC-methanol mixtures. The amounts of DMC that are used in eachcase are correspondingly higher due to the azeotropic distillation ofthe DMC. The calculated molecular weights of the oligocarbonate diolsproduced by the process according to the invention are then, for examplein the case of 1,6-hexanediol as diol component, between 260 and 15000g/mole, preferably between 300 and 7300 g/mole, particularly preferablybetween 350 and 3000 g/mole. If a diol of heavier or lighter molecularweight is used, then the molecular weights of the oligocarbonate diolsproduced according to the invention are correspondingly higher or lower.

The process according to the invention enables oligocarbonate diols ofthe formula II to be produced having between 7 and 1300, preferablybetween 9 and 600 and particularly preferably between 11 and 300 carbonatoms in the chain, in which R1 is used as a symbol for aliphatic diolswith between 3 and 50, preferably between 4 and 40, and particularlypreferably between 4 and 20 carbon atoms in the chain.

The diols may additionally contain ester, ether, amide and/or nitrilegroups. Preferred are diols or diols with ester groups, such as areobtained for example by the use of caprolactone and 1,6-hexanediol. Iftwo or more diol components are used (for example mixtures of variousdiols or mixtures of diols with lactones), then two adjacent groups R1in a molecule may be completely different from one another (statisticaldistribution).

The process according to the invention permits the reproducibleproduction of high-grade oligocarbonate diols from DMC with goodspace-time yields under high conversion rates of the DMC.

The oligocarbonate diols produced by the process according to theinvention may be used for example to produce plastics materials, fibres,coatings, lacquers and adhesives, for example by reaction withisocyanates, epoxides, (cyclic) esters, acids or acid anhydrides. Theymay also be used as binders, binder constituents and/or reactivediluents in polyurethane coatings. They are suitable as structuralelements for moisture-hardening coatings, and as binders or binderconstituents in solvent-containing or aqueous polyurethane coatings.They may furthermore be employed as structural elements for polyurethaneprepolymers containing free NCO groups, or in polyurethane dispersions.

The oligocarbonate diols produced by the process according to theinvention may also be used to produce thermoplastics materials such asaliphatic and/or aromatic polycarbonates, thermoplastic polyurethanes,etc.

EXAMPLE 1 Normal Pressure Apparatus

The normal pressure experiments were carried out in a 6 literdouble-walled, cylindrical, oil-heatable flat-flange pot with floordischarge. The reaction pot is provided with a steel gassing stirrerpassing through a flat-flange cover. The gassing stirrer may eitheraspirate the gas phase in the reaction space and re-pump it, or may feedonly fresh nitrogen from outside into the reaction solution. Expelledgas is then removed from the reactor and is not re-pumped. The reactionpot is rendered inert with nitrogen during the whole reaction time. TheDMC addition (or addition of DMC-MeOH mixtures) is effected by a Telabpump through a dipping tube passing through the flat-flange cover.

Either a 22 cm Vigreux column or a 90 cm packed column filled withRaschig rings (glass, 4×4 mm) is mounted on the flat-flange cover,followed by a Claisen bridge with collecting flask, gas wash flask andcold trap, or alternatively for vacuum treatment a Claisen bridge, gaswash flask, 3 cold traps in series and a rotary-gate valve pump withwhich a vacuum of 15 mbar can be produced are mounted directly on theflat-flange cover.

The DMC contents of the distillates were determined by analytical gaschromatography. All percentage figures are percentages by weight.

The degree of utilisation of the terminal OH groups was determined bymeasuring the methanol present as ester: after complete saponificationof the respective oligo-carbonate diol the methanol content wasdetermined by analytical gas chromatography (Headspace). The differencewith respect to the methanol content before the saponificationrepresents the methanol content bound as ester.

EXAMPLE 2 Production of an Oligocarbonate Ester Diol With MultipleReplenishment of DMC

The aim is to produce an oligocarbonate ester diol from hexanediol-1,6and ε-caprolactone with a predetermined ratio of diol to carbonate of8:7.

The apparatus is described in Example 1. 1890.84 g of hexanediol-1,6 (16moles), 1826.33 g of α-caprolactone (16 moles) and 0.37 g of titaniumtetraisopropylate (17 ppm Ti referred to the diol components) areweighed out into the reaction pot. The diol components are melted,homogenised and heated under nitrogen at 160° C. A total of 1261.12 g ofDMC (14 moles) are required for the conversion, and are added in atwo-stage procedure.

In the 1^(st) stage a mixture of 281.3 g of DMC and 600.3 g MeOH (881.6g of solution with 31.91% DMC) which was azeotropically distilled off ina previous reaction batch is used. This mixture is added within 24.5hours at 160° C. and under normal pressure. 677.65 g of a mixture ofDMC/MeOH containing 7.83% DMC (53.03 g DMC) are distilled off via theshort 22 cm Vigreux column.

In the 2^(nd) stage 980.07 of DMC are metered in within 8 hours. 825.5 gof a DMC-MeOH mixture containing 35.29% DMC (291.36 g DMC) are distilledoff via the 90 cm long packed column.

344.39 g of DMC that were missing according to the desired stoichiometryhad accordingly been distilled off in the two stages. A total of 408.0 gof DMC was therefore subsequently added within 3.5 hours at 160° C.After completion of the addition the batch was heated to 200° C. inorder to complete the reaction. A mixture of 175.20 g of DMC/MeOH thatcontained 32.91% DMC (57.66 g DMC) was distilled off via the largecolumn. Altogether a further 10.0 g of DMC were added at 200° C. within8 minutes. 6.9 g of DMC/MeOH mixture containing 31.02% DMC (2.14 g DMC)were distilled off. A total of 13.81 g too much DMC were accordinglymetered in.

In order to expel the last methanol residues and to utilise the terminalOH groups, 1 l/h of nitrogen was first of all passed into the reactionsolution through the gassing stirrer, which was operating at 480revs/min., followed by 2 l/h N₂ for 4 hours and then 40 l/h N₂ for 5hours. A total of 277.3 g of a DMC/MeOH mixture containing 12.6% DMC(35.09 g DMC) were distilled off. 21.28 g of DMC were accordinglymissing according to the predetermined stoichiometry.

A clear, slightly yellowish product with a degree of utilisation of theterminal OH groups of 99.1% was obtained.

EXAMPLE 3 Production of an Oligocarbonate Ester Diol by Single Additionof DMC

The aim is again to produce an oligocarbonate ester diol fromhexanediol-1,6 and ε-caprolactone, in which the complete amount of DMCis to be added in the 2^(nd) stage. The specified stoichiometry is againdetermined by the diol-carbonate ratio of 1.143, which leads to aproduct having a calculated average molecular weight of 2040 g/mole andan OH number of 55.

The apparatus is described in Example 1. The stirrer speed was increasedto 1500 min⁻¹. 1890.84 g of hexanediol-1,6 (16 moles), 1826.33 g ofe-caprolactone (16 moles) and 0.37 g of titanium tetraisopropylate (17ppm Ti referred to the diol components) were weighed out into thereaction pot. The diol components were melted, homogenised and heatedunder nitrogen at 160° C. A total of 1261.12 g of DMC (14 moles) wererequired for the conversion, and were added in a two-stage procedure.

A mixture of 281.3 g of DMC and 600.3 g of MeOH (881.6 g of solutioncontaining 31.9% DMC) was used in the first stage. This mixture wasadded over 24.75 hours at 160° C. and under normal pressure. 558.02 g ofa mixture of DMC/MeOH containing 6.43% DMC (35.89 g DMC) were distilledoff via the short 22 cm Vigreux column.

1380.07 g of DMC were metered in within 13 hours in the second stage.The temperature of the reactor was then raised to 200° C. anddistillation was continued for a further 2 hours. 1007.00 g of aDMC/MeOH mixture containing 32.21% DMC (324.39 g DMC) were distilled offvia the long 90 cm packed column.

A total of 1661.37 g of DMC were metered in in the two stages. 360.28 gwere distilled off, which means that an excess of 39.97 g of DMC isstill present.

In order to utilise the terminal OH groups 1 l/hour of nitrogen wasfirst of all passed into the reaction solution through the gassingstirrer for 2 hours at 200° C. and 150 mbar, followed by 2 l/hour of N₂for 4 hours and then 40 l/hour of N₂ for 7 hours. A total of 228.1 g ofa DMC-methanol mixture containing 10.19% DMC (23.25 g DMC) were therebydistilled off. A total of 16.72 g too much DMC had accordingly beenadded.

Part of the product (1391 g) was removed via the floor discharge valveand investigated. As expected, due to the excess of DMC a product isobtained having too high a viscosity and too low an OH number (37). Thedegree of utilisation of the terminal OH groups was ca. 99.9%.

EXAMPLE 4 Production of an Oligocarbonate Ester Diol of PredeterminedStoichiometry by Using an Excess of DMC and Effecting Correction byAddition of the Diol Component

The product from Example 3 was adjusted to the desired stoichiometry byadding further diol components. Since part of the product (ca. 38%) hadalready been removed, the excess of DMC in the remainder was calculatedto be 10.34 g. In order to convert this excess, a further 15.5 g ofadipol and 15.0 g of ε-caprolactone were therefore addedstoichiometrically. The reaction solution was then stirred for 5 hoursat 160° C. under a nitrogen atmosphere. After cooling the reactionmixture a clear, almost colourless product was obtained (2574 g) havingthe following characteristics: OH number: 54, degree of utilisation ofthe terminal OH groups: 99.8%.

EXAMPLES 5-7 Reduction of the DMC Content in the Distilled off Methanolby a Three-Stage Procedure

630.28 g of hexanediol-1,6 (5.33 mole), 608.78 g of ε-caprolactone (5.33mole) and 0.12 g of titanium tetraisopropylate (17 ppm Ti referred tothe diol components) were weighed out into the apparatus described inExample 1, melted, homogenised and heated at 160° C. under nitrogen. 183g of a DMC-methanol mixture containing 4.92% DMC (9.0 g DMC) were addedwithin 4 hours. A DMC-methanol mixture containing 3.0% DMC was distilledoff.

In a second experiment the 4.92% DMC-methanol mixture was added within 8hours. A DMC-methanol mixture containing 2.60% DMC was distilled off. Ina third experiment the mixture was added within 12 hours, a DMC-methanolmixture containing 1.50% DMC being obtained as distillate.

The DMC content could accordingly be reduced to 1.5% to 3% in the firststage of a three-stage process by using the ca. 5% DMC-methanol mixturethat is distilled off in the second stage of a three-stage process.

EXAMPLE 8 Production of an Oligocarbonate Diol by Repeated Repumping ofthe Distillate

1890.84 g of 1,6-hexanediol (16 moles) and 0.18 g of titaniumtetra-isopropylate (17 ppm Ti) were placed in the apparatus described inExample 1 and melted. 881.6 g of a DMC-methanol mixture containing 31.9%DMC (281.3 g DMC) was to be added at 160° C. within 25 hours in thefirst stage, by repumping 12 times: the total DMC-methanol mixture wasadded thereto within 2 hours. A distillate was obtained that stillcontained 27.5% DMC. This distillate was then recycled within 2 hoursand again provided a DMC-depleted distillate (23.7%). This procedure wasrepeated a further 10 times. At each stage the DMC of the distillate wasdepleted still further (see Table 1). After the twelfth repumping a DMCcontent of 5.9% was finally reached. The second stage of the process(addition of DMC) was no longer carried out.

TABLE 1 DMC contents in the distillate under repeated repumpingDistillate DMC Distillate Pump Time No. Content (%) Amount [g] [ml/h][h] 1 27.54 788.7 515  2:15 2 23.65 772.8 515  4:20 3 20.30 761.0 515 6:24 4 17.17 774.1 515  8:53 5 14.55 750.9 515 10:56 6 12.65 748.9 51512:54 7 10.99 744.9 515 14:58 8  9.59 740.0 515 17:10 9  8.32 723.3 51519:02 10   7.36 729.1 515 21:12 11   6.54 717.8 515 23:17 12   5.85713.8 515 25:11

For purposes of comparison the experiment was repeated with a catalystconcentration of 250 ppm Ti (0.025% Ti, corresponding to 2.84 g oftitanium tetraisopropylate). After the first addition of theDMC-methanol mixture containing 31.9% DMC at the same pumping rate, adistillate containing 12.2% DMC was obtained after ca. 2 hours, whichwas re-used. Table 2 shows the DMC contents of the distillates. Alreadyafter 3 recycles the DMC concentration had fallen to 3.5%, and after 4recycles (after ca. 6 hours) had fallen to 2.6%.

TABLE 2 DMC contents in the distillate with repeated repumpingDistillate DMC Distillate Pump Time No. Content (%) Amount [g] [ml/h][h] 1 12.16  442.2 515 2:09 2 5.83 398.1 515 3:37 3 3.51 424.9 515 4:424 2.62 414.7 515 5:56 5 2.65 412.0 515 7:01 6 2.42 383.5 515 8:08 7 2.41383.7 515 9:15 8 2.39 395.6 515 10:24  9 2.35 396.6 515 11:33 

EXAMPLE 9 Production of an Oligocarbonate Ester Diol Based on1,5-Pentanediol

1666.40 g of pentanediol-1,5 (16 moles), 1826.33 g of α-caprolactone (16moles) and 0.37 g of Ti isopropylate (17 ppm Ti referred to the diolcomponents) were added to the apparatus described in Example 1. The diolcomponents were melted, homogenized and heated at 160° C. undernitrogen. A total of 1261.12 g of DMC (14 moles) required for thereaction, and were added in a two-stage procedure.

A mixture of 281.3 g DMC and 600.3 g MeOH (881.6 g of solutioncontaining 31.91% DMC) was used in the first stage. This mixture wasadded within 24.5 hours at 160° C. and under normal pressure. 688.18 gof a mixture of DMC/MeOH containing 6.34% DMC (43.65 g DMC) wasdistilled off via the short 22 cm Vigreux column.

In the second stage 1330.07 g of DMC were metered in within 6.5 hours.The temperature of the reactor was then raised to 200° C. anddistillation was continued for a further 2 hours. 1975.84 g of aDMC/MeOH mixture containing 33.92% DMC (331.04 g DMC) were distilled offvia the long 90 cm packed column.

Since there was therefore a total deficit of 24.44 g of DMC relative tothe specified stoichiometry, a further 60.0 g of DMC were added at 200°C. 34.6 g of a DMC-methanol mixture containing 27.84% DMC (9.63 g DMC)were distilled off.

In order to utilise the terminal OH groups 1 l/h of nitrogen was firstof all passed into the reaction solution through the gassing stirrer for2 hours at 200° C. and 150 mbar, followed by 2 l/h of N₂ for 4 hours andthen 40 l/h of N₂ for 5 hours. A total of 208.2 g of a DMC-methanolmixture containing 9.66% DMC (20.12 g DMC) were distilled off A total of5.81 g too much DMC had accordingly been added.

4086.8 g of a slightly pale yellow product having an OH number 62 wereobtained. The degree of utilisation of the terminal OH groups was 99.9%.

EXAMPLE 10 Pressure Apparatus

The pressure experiments were carried out in a 2 l capacity autoclavethat was equipped with an electric stirrer and a dipping tube for addingthe DMC. Nitrogen may be passed into the reaction solution through thedipping tube either to provide an inert atmosphere above the reactionsolution, or for the de-capping of the terminal groups. The gas mixturedistilled off is separated via two packed columns (25 cm and 80 cm longrespectively) that can be operated appropriately as desired and that canbe heated up to 90° C. via a water thermostat, and is condensed in areflux cooler. The product is discharged from the apparatus via apressure retention valve. The pressure in the apparatus is increasedthrough the nitrogen that is fed in: the nitrogen to be fed in isadjusted (minimum 2 l/hour) via a mass flow regulator, and the pressureretention valve is automatically controlled via a pressure measurementdevice in the apparatus so that only the amount of nitrogen required tomaintain the pressure constant is expended. Distillate that is formed isdischarged together with the nitrogen.

EXAMPLE 11 Production of an Oligocarbonate Ester Diol Under Pressure

An oligocarbonate ester diol is to be produced from hexanediol andε-caprolactone with a predetermined ratio of diol to carbonate of 8:7.

630.28 g of hexanediol-1,6 (5.33 moles), 608.78 g of ε-caprolactone(5.33 moles) and 0.123 g of Ti isopropylate (17 ppm Ti referred to thediol components) were weighed out into the apparatus described inExample 10. The autoclave was pressurised (2 bar) with 3 l/h ofnitrogen. The diol components were melted, homogenised and heated to180° C. A total of 420.36 g of DMC (4.67 moles) were required for thereaction, and were added in a two-stage procedure.

A mixture of 39.40 g of DMC and 179.0 g of MeOH (218.4 g of solutioncontaining 18.04% DMC) was used in the first stage. This mixture wasmetered in within 10 hours at 2 bar and at an internal temperature of180° C. 96.1 g of a mixture of DMC/MeOH containing 3.64% DMC (3.50 gDMC) was distilled off via the small column (25 cm, 80° C.). Low DMCcontents in the distillate were thus achieved in a significantly shortertime than in the experiments carried out under normal pressure.

In the second stage 437.20 g of DMC were metered in within 7 hours at180° C. The DMC-methanol azeotrope was distilled off via the largecolumn (80 cm, 80° C.).

After adding the DMC the reactor temperature was raised to 200° C., thecolumn temperature to 85° C., and the mixture was distilled for afurther 3 hours. A further 20 g of DMC were added and the whole wasdistilled for 2 hours. A total of 337.40 g of a DMC-methanol mixture wasdistilled off, which contained 19.62% DMC (66.21 g DMC).

The utilisation of the terminal groups was effected by passing in 25 l/hof nitrogen through the simple dipping tube at 70 mbar within a periodof 40 hours. 54.50 g of a DMC-methanol mixture containing 11.97% DMC(6.52 g) were distilled off.

A product was obtained having an OH number of 80 and a degree ofutilisation of the terminal groups of 99.8%.

EXAMPLE 12 Production of an Oligocarbonate Diol Under Pressure

An oligocarbonate diol was to be prepared from hexanediol with apredetermined ratio of diol to carbonate of 1.294.

822.9 g of hexanediol-1,6 (6.96 moles) and 82 mg of Ti isopropylate (17ppm Ti referred to the diol components) were weighed out into theapparatus described in Example 10. The autoclave was pressurised (2 bar)with 3 l/h of nitrogen. The diol components were melted, homogenised andheated to 184° C. A total of 484.9 g of DMC (5.38 moles) was requiredfor the reaction, and was added in a two-stage procedure.

In the first stage 264.45 g of a DMC-methanol mixture containing 18.04%DMC (47.7 g DMC) were metered in within 10 hours at 2 bar and at aninternal temperature of 184° C. 165.3 g of a mixture of DMC/MeOHcontaining 5.35% DMC (8.85 g DMC) were distilled off via the smallcolumn (25 cm), which was heated to 80° C.

In the second stage 515.2 g of DMC were metered in within 6.7 hours at184° C., followed by 15 g of DMC within 10 minutes at 198° C. TheDMC-methanol azeotrope was distilled off via the large column (80 cm,80° C.). A total of 402.10 g of a DMC-methanol mixture containing 17.90%DMC (71.99 g DMC) were distilled off.

The utilisation of the terminal groups was effected by passing in 5 l/hof nitrogen through the simple dipping tube at 70 mbar and 200° C.within a period of 26 hours. 30.90 g of a DMC-methanol mixturecontaining 5.73% DMC (1.77 g DMC) were distilled off.

A product was obtained having an OH number of 255, a melting point of38° C. and a degree of utilisation of the terminal groups of 99.8%.

EXAMPLE 13 Varying the Catalyst Concentration

The experiment of Example 3 was repeated, halving the catalystconcentration (0.186 g of titanium tetraisopropylate, 8 ppm Ti). Onadding the DMC-methanol mixture (881.6 g, 31.91% DMC) within 24 hours at160° C. a DMC-depleted mixture containing ca. 10.2% DMC was obtained inthe first stage of the process according to the invention.

The experiment was repeated at 185° C. On adding the DMC-methanolmixture (31.91% DMC) a distillate containing 8.0% DMC was obtained inthe first stage within 24 hours.

At 195° C. a distillate containing 6.7% DMC was obtained on adding theDMC-methanol mixture (31.91% DMC).

EXAMPLE 14 Production of an Oligocarbonate Ester Diol Under Pressure

The aim is to produce an oligocarbonate ester diol from hexanediol-1,6and ε-caprolactone on an industrial scale. The predeterminedstoichiometry is determined by the diol-carbonate ratio of 1.143, whichleads to a product having a calculated, average molecular weight of ca.2040 g/mole and an OH number of 55.

A 200 l capacity vessel equipped with a blade stirrer was provided witha 2.5 m long packed column (Ø11 cm, filled with baffles), attachedcooler and a 100 l receiver. Distillates collected in the receiver canbe recycled to the reactor via an immersed pump through a floor flange.

62.353 kg of adipol (0.528 kmole), 60.226 kg of caprolactone (0.528kmole) and 12 g of titanium tetraisopropylate (17 ppm Ti) were placed inthe reactor, rendered inert under nitrogen, heated to 80° C. andhomogenised. 41.612 kg of DMC (0.462 kmole) are accordingly required toachieve the predetermined stoichiometry.

44 kg of the DMC-methanol mixture from the previous batch (23.0% DMC,10.1 kg DMC) were added to the receiver. The pressure in the apparatuswas adjusted to 5.2 bar and the contents were then heated further to194° C.

The DMC-methanol mixture from the receiver was metered in underneath theliquid level into the stirred vessel within one hour (pumping rate ca.40 l/h). Distillate formed during the metering in was recycled directlyto the receiver, where it was mixed with the original DMC-methanolmixture from the previous batch. This mixture was recycled for a furtherthree hours. DMC-methanol mixture was thus continuously metered into thereactor, a DMC-depleted mixture being distilled off and collected in thesame collection vessel, with the result that the DMC concentration fellover time. After a total of 4 hours the metering in was stopped and thereaction mixture was distilled for a further 2 hours.

This distillate was then collected in the receiver and discarded. ADMC-methanol mixture (42.0 kg) containing 5.3% DMC (2.2 kg) wasobtained.

47.0 kg of DMC were then added to the receiver. The DMC was added at196° C. within one hour to the vessel and then—as previouslydescribed—recycled by pumping for five hours. The distillate was thencollected within 2 hours at 200° C. 51.1 kg of a DMC-methanol mixturecontaining 25.3% DMC (12.9 kg DMC) were collected.

The pressure in the apparatus was then reduced to normal pressure,following which the pressure was slowly reduced to 100 mbar and themethanol residues were distilled off over 32 hours in order to de-capthe terminal groups.

After discarding the first runnings and remaining residues in thereactor, 116 kg of a clear, pale yellowish product were obtained. The OHnumber was 58. A correction by adding further amounts of the diol wasnot performed. The degree of utilisation of the terminal OH groups was99.6%.

Detailed Analysis of DE-A 198 29 593

According to DE-A 198 29 593 a diol component is placed in the reactorand an oligocarbonate diol is obtained by adding DMC and distilling offmethanol. The reaction time is ca. 4 hours (Examples 1 and 2). Molarratios of methanol to DMC of 0.5:1 to 99:1 in the distillate (claim 1c)are achived. This corresponds to DMC contents of 85 to 2.8 wt. %.

DE-A 198 29 593 does not disclose that the amount of DMC used is reducedby azeotropically distilled-off DMC and therefore no longer agrees withthe predetermined stoichiometry and accordingly has to be corrected.

The fact that considerable amounts of DMC are distilled off and have tobe replenished can be deduced from the examples:

Thus, in Example 1 an oligocarbonate diol is produced from 918 kg (3920moles, mol. wt. =234.2 g/mole) of a diol (polyTHF) and 440 kg of DMC(4885 mole, 90.1 g/mole). The carbonate is in this case added in a molarexcess. On account of the reversed ratio of diol to DMC an oligomershould therefore be produced whose terminal groups should consist ofmethoxycarbonyl terminal groups as described in formula III, where R1denotes —(CH₂)₄—.

An oligocarbonate diol with terminal OH groups, as was obtained as endproduct, can accordingly only be produced if, during the distillation ofthe methanol, so much DMC has been lost that the quantitative ratios ofDMC and diol have reversed once more, i.e. that effectively more diolthan DMC has been used. An amount of at least 965 moles (4885−3920) DMC(87 kg) must therefore have been distilled off. This corresponds to ca.20% of the DMC that was used. After distilling off this amount only thegel point is reached however, which should lead to a completepolymerisation. In order to obtain the oligocarbonate diol that wasformed, even larger amounts must therefore have been distilled off.

The effective quantitative ratios can be calculated from the determinedOH number of the diol that was formed:

according to formula IV, in which n denotes the OH functionality of theoligomer (in this case n=2), the average molecular weight can bedetermined from the OH number.

molecular weight=(56106·n)/OH No.  (IV)

From the OH number of the oligocarbonate diol that was formed, namely 44Mg_((KOH))/g_((diol)), an average molecular weight of 2550.25 g/mole canbe calculated, corresponding to an average composition of 9.9 diol unitsand 8.9 carbonate units per molecule. 3920 moles of diol have thereforereacted with only 3524 moles of DMC (=3920×8.9/9.9). Consequently 1361moles (4885-3524) of DMC have been azeotropically distilled off. ThisDMC loss therefore accounts for, on average, ca. 27.8% of the DMC used.The distillate consequently consisted of 1361 moles of unreacted DMC(122.5 kg) and 2×3524 moles of MeOH (225.5 kg/two molecules of methanolare formed per molecule of DMC). This leads to a DMC content of ca. 35wt. % in the distillate.

The necessary correction amounts had therefore already been taken intoaccount in the weighing out, contrary to what had been stated. TheDMC-methanol mixture was by and large distilled off as an azeotrope.

Claim 1b also points to the azeotrope problem: a 5-fold excess of DMC,as is disclosed in claim 1b, can be explained only by the need forcorrection amounts: already starting with a 2-fold excess, in fact onlythe 2:1 ester is formed, as shown in formula V, where R1 denotes—(CH₂)₄—.

At a ratio of 1:1 even the gel point is reached, in which a completepolymerisation takes place if the DMC amount has not been reduced byazeotropic distillation.

It must therefore be assumed that in DE-A 198 29 593 azeotropicDMC-methanol mixtures are distilled off, and that the amount of DMCdistilled off was already taken into account in the weighing outprocedure.

COMPARISON EXAMPLE 1 One-Stage Addition of DMC

In DE-A 198 29 593 the reaction of DMC with a diol is carried out in aone-stage process with reaction times of 4 hours at 140 to 200° C. andat a catalyst concentration of 0.15% or 0.12% Ti(O-nBu)₄ (Examples 1 and2). This corresponds to concentrations of 211 and 170 ppm respectivelyof Ti. At these high catalyst concentrations the catalyst must beneutralised by adding phosphoric acid after the end of the reaction.

For purposes of comparison with DE-A 198 29 593 the one-stage variantwas investigated, in which the total amount of carbonate required isadded in one stage as DMC. A DMC-methanol mixture is distilled offduring the whole course of the experiment. In each case distillation wasperformed only via a short Vigreux column in order to exclude columneffects (change in the composition due to rectification). The azeotropiccomposition (ca. 30% at normal pressure) is in fact obtained in eachcase at the end of a large packed column.

1890.84 g of hexanediol-1,6 (16 moles) and 0.18 g of Ti isopropylate(0.01% Ti(O-iPr)₄, i.e. 17 ppm Ti referred to the diol component) wereweighed out into the apparatus described in Example 1, melted under anitrogen atmosphere, homogenised and heated to 160° C. To carry out thereaction 1261.12 g of DMC (14 moles) were metered in within 24 hoursunder a constant pump output. A DMC-methanol mixture (872.4 g) with aDMC content of 38.1% was distilled off via the short column. Thecomposition fluctuated only slightly over the whole course of theexperiment, and the DMC contents of the distillates were always between37.3% and 40.4%. A total of 332.4 g of DMC were thus azeotropicallydistilled off, which were added in a subsequent stage within 6.3 hoursat the same pump output. A DMC-methanol mixture containing 41.2% DMC wasdistilled off once more.

The experiment was repeated with the pump outputs halved: the reactiontime—the first addition of the total amount of DMC without correctionamounts in a subsequent stage—was now 51 hours. A DMC content of 29.8%in the distillate was achieved. A further doubling of the reaction timeto 108 hours led to a DMC content of 22.3% in the distillate (see Table3). With a reaction time of 9 hours a DMC content of ca. 96% in thedistillate was obtained.

Further similar experiments were carried out with a 15-fold catalystconcentration—as was employed in DE-A 198 29 593. The results are alsoshown in Table 3.

TABLE 3 DMC contents in the distillate as a function of the reactiontime and amount of catalyst Catalyst Concentration Reaction time 0.01%0.15% 0.15% (1^(st) stage without Ti(O-iPr)₄ Ti(O-iPr)₄ Ti(O-nBu)₄subsequent stage) (17 ppm Ti) (250 ppm Ti) (DE-A 198 29 593)  4 hoursca. 25.5% ca. 35%  9 hours ca. 96%  24 hours ca. 38.1% Ø ca. 10.4%*⁾  51hours ca. 29.8% 108 hours ca. 22.3% *⁾Increasing DMC content from 5.7%at the start to 18.3% at the end of the experiment

The experiment involving a reaction time of 9 hours (catalystconcentration 0.01% Ti(O-iPr)₄ i.e. 17 ppm Ti) shows that, under theseconditions, the transesterification is the velocity-determining stage:DMC is added so quickly that it is directly distilled off again withoutreacting (ca. 96%). The distillation rate is significantly greater.

With increasing reaction time and slower metering in of the DMC, thedistillation becomes slower and the transesterification itself becomescompetitive. The DMC is depleted due to reaction (transesterification),and the DMC fractions in the distillate fall to for example Ca. 22.3% at108 hours' reaction time.

The experiment involving a reaction time of 9 hours also shows theeffect of a large column: without large packed columns the DMCconcentrations established at the head of the reactor are obtained. AsExamples 2 and 3 show, the DMC is depleted further in a packed column,the azeotrope is then obtained at the head of the column also with shortreaction times, and DMC is separated in the column and recycled to thereactor.

The transesterification is greatly accelerated by increasing thecatalyst concentration by a factor of 15 (0.15% Ti(O-iPr)₄ i.e. 250 ppmTi), whereas the distillation rate remains constant. At constantreaction times this leads to a preferred reaction of the DMC, with theresult that the DMC content in the distillate fall sharply (e.g. from38% to on average 10.4% at a reaction time of 24 hours, see Table 3). Areduction of the reaction time then leads in turn to a higher DMCcontent in the distillate (ca. 25.5% at 4 hours' reaction time and 0.15%catalyst) due to acceleration of the distillation, while an increase inthe reaction time leads to a higher DMC conversion and thus to lower DMCcontents in the distillate.

The experiment with a reaction time of 24 hours and a catalystconcentration of 0.15% Ti(O-iPr)₄ i.e. 250 ppm Ti) shows that the DMCcontent of the distillate rises with increasing reaction time. Table 4shows this rise in the DMC concentration of the distillate. The amountsof distillate formed per unit time were constant. The average DMCcontent of all distillates was 10.4%.

TABLE 4 DMC content in the distillate as a function of time at areaction duration of 24 hours and a catalyst concentration of 0.15%Ti(O-iPr)₄ Time DMC Contents in Distillate [h] [%]  3:12  5.72  5:00 5.70  7:57  6.41  9:34  7.16 11:31  8.06 14:28  9.43 16:15 10.90 17:4912.30 20:19 14.25 24:00 18.31

The distillation rate remains constant during this experiment (equalamounts of distillate per unit time). An increasing DMC content can beexplained by the decrease in the rate of reaction of the DMC: pure dioland DMC are present at the start of the experiment, and thetransesterification equilibrium is displaced to the maximum extent. Thedriving force to achieve equilibrium through a chemical reaction ishigh, and the transesterification is quick. As the reaction proceedsover time the system approaches equilibrium and the driving force toachieve further transesterification decreases. Accordingly the reactionrate of the transesterification slows down in contrast to the constantdistillation, and the DMC content in the distillate constantlyincreases. When this behaviour was not observed or only to a minorextent in the other experiments (increase in the DMC content by ca. 1percentage point), this reflects the higher DMC content already presentat the start (23-30%).

This sharp rise in the DMC content is not observed with a multistageprocess according to the invention, since in the first stage only ca. ⅓of the total amount of DMC in the form of the DMC-methanol mixture isavailable from a previous batch. Accordingly, in this experiment too(see Table 4) a DMC content of only 5% to 6% in the distillate wasachieved during the first 8 hours.

Claim 1c of DE-A 198 29 593 discloses a DMC content of the distillate of85 to 2.8 wt. %. As the Comparison Examples show, a DMC content of ca.3% should be very easy to achieve: at high catalyst concentrations andlong reaction times a DMC content of ca. 5% in the distillate can beachieved without any difficulty at the start of a batch, and with longerreaction times or higher catalyst concentrations even lower DMC contentscan be achieved.

These low DMC losses are achieved however only by such a high catalystconcentration that the catalyst has to be neutralised or separated afterthe end of the reaction, which is a complicated procedure. In addition,the DMC loss due to attainment of the transesterification equilibriumrises with increasing reaction time. Permanently low DMC contents in thedistillate can accordingly be achieved at the end of the reaction timeonly under extremely long reaction times.

If the amount of catalyst is reduced to such an extent that it can beleft in the product (less than 0.01% Ti(O-iPr)₄ i.e. 17 ppm Ti), thensmall DMC contents in the distillate cannot feasibly be achieved. Thus,even with a reaction time of more than 100 hours the DMC content can bereduced only to ca. 22%. In order to achieve a further reduction in theDMC content in the distillate at catalyst concentrations that cansubsequently be left in the product, a further, no longer practicableincrease in the reaction time is necessary.

What is claimed is:
 1. A multistage process for the production ofaliphatic oligocarbonate diols characterized in a degree of conversiongreater than 80% comprising reacting at least one aliphatic diol withdimethyl carbonate (DMC), optionally accelerated by catalysts, whereinthe dimethyl carbonate is introduced into the reaction in at least twosuccessive stages and where in at least the first stage of the processdimethyl carbonate is introduced in the form of its mixture withmethanol.
 2. Process according to claim 1 characterised in that thereaction of DMC and aliphatic diols is carried out in two stages,wherein DMC-methanol mixtures that have been distilled off from aprevious batch are used in a first stage with further utilisation of thecontained DMC, and pure DMC is used in a second stage, a DMC-methanolmixture being distilled off that is collected and re-used in the firststage in a following batch.
 3. Process according to claim 1characterised in that the reaction of DMC and aliphatic diols is carriedout in three stages, wherein the DMC-methanol mixture containing only asmall proportion of DMC that has been distilled off from the secondstage of a previous batch is used in a first stage, with almost completeutilisation of the contained DMC, and the DMC-methanol mixture that hasbeen distilled off in the third stage of a previous batch is used in asecond stage, with utilisation of the contained DMC and distilling-offof a DMC-methanol mixture with a small proportion of DMC, which iscollected and used in the first stage in a following batch, and pure DMCis used in a third stage, a DMC-methanol mixture being obtained that iscollected and re-used in the second stage in a following batch. 4.Process according to claim 1 characterised in that the total amount ofDMC represented by the sum of the partial amounts of DMC used in eachcase in all stages, less the amounts of DMC that are distilled offduring the overall reaction, corresponds to the total amount of DMC thatis predetermined by the stoichiometry of the desired product, whereinafter the in each case last stage of the process the missing amounts ofDMC that have previously been distilled off are additionally added orare additionally used in the in each case last stage in which pure DMCis added.
 5. Process according to claim 1 characterised in that anexcess of DMC is used, the oligocarbonate diol that is formed isde-capped, and the desired stoichiometry of the oligocarbonate diol isthen correctly adjusted by adding the corresponding amounts of the diolcomponents and renewed esterification.
 6. Process according to claim 1characterised in that the molar ratio of diol to DMC in the productpredetermined by the stoichiometry of the desired end product is between1.01 and 2.0.
 7. Process according to claim 1 characterised in that thereaction of DMC with aliphatic diols is carried out at pressures between0.4 and 100 bar, and at temperatures from 100° C. to 300° C.
 8. Processaccording to claim 1 characterised in that it is carried out batchwiseor continuously.
 9. Process according to claim 1 characterised in thataliphatic diols with 3 to 20 C atoms in the chain, as well as mixturesof various diols, are used.
 10. Process according to claim 1characterised in that addition products of the diols with lactones(ester diols) such as for example caprolactone, valerolactone etc., aswell as mixtures of the diols with lactones, are used.
 11. Processaccording to claim 1 characterised in that addition products of thediols with dicarboxylic acids, such as for example adipic acid, glutaricacid, succinic acid, malonic acid etc., or esters of the dicarboxylicacids as well as mixtures of the diols with dicarboxylic acids or estersof the dicarboxylic acids, are used.
 12. Process according to claim 1characterised in that polyether polyols such as for example polyethyleneglycol, polypropylene glycol, polybutylene glycol are used.
 13. Processaccording to claim 1 characterised in that hexanediol-1,6 or mixtures ofhexanediol-1,6 and caprolactone are used.
 14. Process according to claim10 characterised in that the ester is formed in situ from the startingmaterials during the oligocarbonate-diol preparation without preliminarytransesterification.
 15. Process according to claim 1 characterised inthat all known soluble catalysts for transesterification reactions(homogeneous catalysis) are used.
 16. Process according to claim 1characterised in that soluble catalysts are used in concentrations up to1000 ppm (0.1%).
 17. Process according to claim 1 characterised in thatthe catalyst is left in the product, separated, neutralised or maskedafter the end of the reaction.
 18. Process according to claim 1characterised in that heterogeneous transesterification catalysts areused (heterogeneous catalysis).
 19. Process according to claim 1characterised in that the terminal OH groups are de-capped after the endof the reaction by removing the last residues of methanol by applying avacuum.
 20. Process according to claim 1 characterised in that thede-capping of the OH terminal groups after the end of the reaction(distillation) is effected by expelling the last residues of methanoland completing the transesterification by passing inert gas bubbles intothe reaction mixture, optionally under application of a vacuum. 21.Process according to claim 1 characterised in that the methanolcontaining and dimethyl carbonate-containing/gas stream leaving theoligocarbonate is partially added again to the oligocarbonate for thesaturation.
 22. Process according to claim 1 characterised in that thede-capping of the terminal OH groups after the end of the reaction(distillation) is carried out by passing inert gases such as nitrogen,argon, methane, ethane, propane, butane, dimethyl ether, dry natural gasor dry hydrogen, etc. into the reactor and generating gas bubbles in thereactor, optionally under the application of a vacuum.
 23. Processaccording to claim 1 characterised in that the de-capping of theterminal OH groups after the end of the reaction (distillation) iseffected by passing low boiling point, inert liquids such as pentane,cyclopentane, hexane, cyclohexane, petroleum ether, diethyl ether ormethyl tert.-butyl ether, etc. into the reactor and generating gasbubbles in the reactor optionally under the application of a vacuum,wherein the above substances may be introduced in liquid or gaseousform.
 24. Process according to claim 19 characterised in that thede-capping is carried out at temperatures of 130° C. to 300° C. and atpressures of 0.01 mbar to 10 bar.